[tsimionescu]

I'm not talking just about transportation, I'm also talking about the technology required to make an actually self-sustaining human colony anywhere outside the Earth. That is the part that only exists in principle - when you go to the details, we don't actually have any idea how we could build even a Mars colony that is truly self-sustaining, never mind one on a more inhospitable world.

Note that when I say self-sustaining, I don't just mean power, food, air, and water. I mean everything that a high-tech colony actually needs - plastics, machined parts, microprocessors, software, and so on.